The Mount Desert Island Biological Laboratory (MDIBL), a 109-year-old non-profit research institution, is widely regarded as a leading international center for biomedical research using marine and freshwater organisms as model systems. MDIBL has a long-standing, world-renowned seasonal research program, and expanding federally-funded year-round research and research training efforts. Research organisms are currently maintained in flow through seawater holding facilities that were built in the 1970s, or in aquaria maintained in individual laboratories. While these systems were adequate in the past, they have deteriorated with age and require modernization. Moreover, researchers at MDIBL are now routinely employing a wide variety of aquatic model organisms in addition to the traditional elasmobranch and teleost models, including zebrafish, sea urchins, crabs and lobsters. Optimal care and use of all these species requires a greater degree of environmental control than is possible with the current facilities. The recent growth of MDIBL's research community, coupled with research and animal care requirements for more controlled environmental conditions, necessitates critical improvements to our holding facilities. The proposed improvements will (1) enhance the quality of the seawater that is distributed to all laboratories and holding facilities, (2) optimize environmental conditions for marine and freshwater organisms, and (3) create a more efficient layout and design of two holding facilities and upgrade their engineering elements. The result will enhance MDIBL's animal care capabilities, facilitate continued growth and recruitment of scientific groups, and ensure the continued excellence of research and research training at MDIBL. [unreadable] [unreadable] [unreadable]